In the case of increased safety requirements, electronic lock systems are used which operate, for example, by means of electromagnetic waves. In particular in the case of motor vehicles, such lock systems are used as door lock systems for access authorization.
Such lock systems are known from DE 43 40 260 A1. The lock system is composed of a first device, which has at least two states and is embodied as a control device for locking and/or unlocking the car doors, the tailgate or the like, and an associated second device which is embodied in the manner of an electronic key. The two devices have, for their intended operation, transmitters and/or receivers for transmitting electromagnetic signals. During the intended operation, at least one signal can be transmitted between the key and the control device as an encoded operating signal for authenticating the key with the result that after positive evaluation of the transmitted operating signal and therefore when the key is authorized it is possible to bring about a change in the state of the control device.
In the motor vehicle, there is a chargeable vehicle battery for supplying the electrical components of the motor vehicle with electrical energy. This vehicle battery, therefore, also serves as a first energy store for supplying energy to the first device for the intended operation thereof. In the key, there is also a key battery which generally cannot be charged, as a second energy store for supplying energy to the second device for the intended operation thereof. In the case of an exhausted vehicle battery or an exhausted key battery, the lock system is not functionally capable, with the result that access to the motor vehicle is no longer possible. For this emergency situation, a mechanical lock which permits access to the motor vehicle by means of a mechanical emergency key has been integrated into the car door until now. However, the mechanical lock and the mechanical emergency key are costly and merely provide a low level of protection against theft.